The Long-Term Impact of Pipeline Construction on Solonetzic Mixed Prairie

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  • In 1981, a study was initiated near Princess, Alberta to evaluate single-lift pipeline construction impacts on Solonetzic mixed prairie rangeland. In August 1991, a further evaluation of the study sites was conducted to determine the longevity of the changes that took place on the 1981 right-of-way from using 1981 construction techniques. The study concentrated on the well-documented 1981 right-of-way, and compared it to the oldest trench, installed in 1957, and to the undisturbed adjacent mixed prairie.
    It was still evident in August 1991, that single-lift pipeline construction in Solonetzic mixed prairie had significant effects on soil chemical, soil physical, hydrologic, and vegetative parameters of the ecosystem. Effects were similar to those documented in 1983. As in the first study, these effects and their changes over time were in turn affected by both the grazing regime imposed on the rangeland and the different construction activities at the time of pipeline installation, with trenching having the most significant impact. However, there was a distinct trend towards predisturbed conditions evident in many vegetation and soil chemical and physical parameters.
    In August 1991, on the 1981 right-of-way vs the undisturbed prairie there was still increased surface bulk density and surface water; increased organic carbon, pH and sodium adsorption ratio to depths of 15 cm, and electrical conductivity to depths of 45 cm. Calcium, magnesium, sodium, sulphate, and chloride were decreased to 45 cm, and potassium below 5 cm. Soil bulk density with depth decreased in trench treatments and increased on work and stockpile treatments. In the trench, penetration resistance and depth to maximum penetration resistance decreased and soil water with depth increased. Bare ground, the number of introduced and pioneer (weedy) species, and cover of little club moss increased; species diversity and number of native species decreased.
    A trend towards predisturbed conditions was evident on the rights-of-way from 1983 to 1991, although the magnitude of change was often small and not always statistically significant. The trend was characterized by decreased bare ground, increased species diversity and native species, and decreased native pioneer species. Downward salt movement in the 1981 trench and 1981 stockpile treatments was evidenced by decreases in electrical conductivity, sodium, sulphate, and sodium adsorption ratio to 15 cm and increases in these parameters below 15 cm. Soil bulk density at the surface and with depth decreased; there was a slight increase in organic carbon.
    Grazing regime continued to impact the revegetated pipeline rights-of-way by increasing Elymus angustus under early season grazing and increasing Agropyron pectiniforme under late season grazing.

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    TransCanada Pipelines Ltd.